Field of the Invention
The present invention generally relates to the fields of biomedical imaging and obstetrics. Particularly the present invention discloses a dual modality laser optoacoustic-ultrasound imaging system (LOUIS) on a single platform that can provide medically relevant information about the developing placenta and associated tissues.
Description of the Related Art
The placenta and umbilical cord are vital for proper growth and transfer of nutrients and gases to and from the fetus. Several conditions are related to abnormal function of placenta, including abnormal fetal growth, stillbirth, preeclampsia, and preterm birth (1-2). Current in vivo methods of fetal surveillance, including ultrasound tomography (UST) techniques and fetal heart rate monitoring, have proved to have low sensitivities and high false positive rates for adverse pregnancy outcomes (3).
These techniques do not provide information on tissue oxygenation in the placenta which has important implications for both placental development as well as the development of conditions such as preeclampsia and intrauterine growth restriction (IUGR) (4-5). Doppler velocimetry of the uterine, umbilical, and middle cerebral arteries is the only clinically accepted method used during pregnancy to measure blood flow to key organs in the fetal-placental unit during pregnancy. However, oxygenation of the tissue is not measurable by ultrasound and so it is not usable to estimate local placental perfusion. Magnetic resonance imaging (MRI) and near infrared spectroscopy (NIRS) have been used experimentally to evaluate oxygenation, however, there are limitations in those approaches (6-8). Due to cost, logistics, and lack of real-time information, MRI is not feasible for surveillance of the placenta and fetus. NIRS has effectively no imaging resolution and provides only spatially integrated results.
Optoacoustic tomography (OAT) combines optical illumination and high resolution ultrasound detection to achieve deep visualization of live tissues based on optical contrast of blood, which is not degraded by light scattering (9-11). Strong near infrared (NIR) optical absorption of hemoglobin results in a superior optical contrast of blood-rich tissues (12, 13). OAT systems are substantially more cost effective alternatives to conventional MRI modalities, and have demonstrated clinical feasibility in oncology, specifically in applications related to breast and prostate cancer diagnostics (14-16). Multiple wavelengths in NIR region of optical spectra were previously used to demonstrate that OAT imaging can provide high resolution maps of total hemoglobin and blood oxygenation at frame rates close to real-time imaging (17-20). It also could be integrated with a standard clinical ultrasound imaging system such that the same probe detects ultrasonic and optoacoustic response of the tissue (15,17,21).
Thus, there is a need in the art for improved methods of monitoring placental function in vivo. Particularly, a need exists for cost effective imaging systems that can be used simultaneously with current methods of ultrasound for a real time assessment of blood oxygenation in the developing placenta and umbilical cord. Specifically, the prior art is deficient in a dual modality laser optoacoustic-ultrasound imaging system and methods of use for high contrast and high resolution visualization and coregistered functional and anatomical mapping of the placenta and associated tissue. The present invention fulfills this longstanding need and desire in the art.